A team of astronomers has discovered two distant moons orbiting around the planet Uranus.
"This discovery is significant because Uranus was the only giant planet without distant moons on irregular orbits," says Brett Gladman of the Canadian Institute for Theoretical Astrophysics at the University of Toronto and the lead investigator on the team that made the discovery.
Other members of Gladman's team of astronomers are Philip Nicholson and Joeseph A. Burns of Cornell University and J.J. Kavelaars of McMaster University.
All giant planets in our solar system have regular and irregular satellite systems. Regular satellites orbit near the planet's equator, while irregular satellites orbit out of this plane. Until now, Uranus was the only giant planet with no known distant moons circling it on irregular orbits.
Prior to these discoveries, Uranus had 15 known moons, ten of which were found by the Voyager spacecraft during its 1986 flight through the Uranian system. The other five moons were identified by ground-based telescopes, with the last one being discovered in 1948. These known moons travel along nearly circular equatorial orbits that lie close to the planet, between 50,000 km and 583,000 km away.
The new Uranian satellites are the faintest ever detected without the aid of a spacecraft, and their discoveries were made possible by the use the large Hale 5-metre telescope on Palomar Mountain near San Diego, California.
The findings will be announced by the International Astronomical Union on Friday, Oct. 31.